It is known that in certain procedures of producing aromatic carbonate polymers from dihydric phenols and a carbonate precursor such as phosgene small amounts of certain molecular weight regulators or chain terminators can be used to provide end or terminal groups on the carbonate polymer and thereby control the molecular weight of the polycarbonate. Such materials include phenol and p-tertiary-butylphenol.
The prior art also discloses several other types of compounds that act as chain terminators for the carbonate polymers. Thus, U.S. Pat. No. 3,085,992 discloses alkanol amines as chain terminators; U.S. Pat. No. 3,399,172 teaches imides as chain terminators; U.S. Pat. No. 3,275,601 discloses that aniline and methyl aniline function as chain terminators in the interfacial polymerization process for producing polycarbonates; and U.S. Pat. No. 4,001,184 discloses primary and secondary amines as molecular weight regulators for polycarbonate. Furthermore, U.S. Pat. No. 3,028,365 discloses that aromatic amines and other monofunctional compounds can be used to control or regulate the molecular weight of the polycarbonates, thereby forming aryl carbamate terminal groups. Aromatic polycarbonates having carbamate end groups are disclosed in U.S. Pat. No. 4,111,910. These polycarbonates are prepared using a terminating amount of ammonia, ammonium compounds, primary cycloalkyl, aliphatic or aralkyl amines and secondary cycloalkyl, alkyl or aralkyl amines.
However, according to Schnell, Chemistry and Physics of Polycarbonates (1964), page 183, ammonium hydroxide and amines saponify polycarbonates back to the monomers, i.e., bisphenol A. This is supported by Bolgiano in U.S. Pat. No. 3,223,678 wherein he indicates that small amounts of amines such as monoethanolamine and morpholine break or degrade polycarbonates into lower molecular weight polycarbonates. Thus, this area of chemistry is generally not very well understood and is one where the empirical approach is still generally the method used to determine whether a particular compound or class of compounds will function as effective chain terminators or terminal groups in polycarbonate. This area is yet further complicated by the fact that, even though a particular compound may be a chain terminator, its presence as a terminal group in the polycarbonate polymer adversely affects the physical properties of the polycarbonate.